Japan on tsunami alert after Samoa quake

A tsunami alert was issued for the Pacific shores of Japan after a massive 8.0 magnitude earthquake struck thousands of kilometres away, off the islands of Samoa and American Samoa.

Japan's meteorological agency warned that tsunami waves of up to 50 centimetres would reach the archipelago's Pacific shores.

The first waves were expected to hit the Ogasawara island chain, 1,000 kilometres south of Tokyo, at around 11:00 am (local time), followed by Japan's main island about an hour later, it said.

"We issued a tsunami alert for the nation's entire coastline facing the Pacific. We urge people not to engage in activity in or near the sea as it is very dangerous," said Yasuo Sekita, who heads the agency's quake division.

"We urge people to be on full alert as fishing vessels have been carried away or capsized before," he told a nationally televised news conference.

Tsunami waves less than one metre tall are not known to have caused damage on land before in Japan, according to the agency.

But "waves of 50 centimetres are still fairly dangerous for people in the sea or on the coast," Mr Sekita warned.

The huge earthquake which hit the remote Pacific islands of Samoa and American Samoa killed up to 100 people and wiped out entire villages, sweeping cars out to sea, officials and witnesses said.